This invention relates to the production of doped and multi-component oxide ultrafine- or nano-particles (i.e. particles of less than 1 micron and preferably in the size range of 5–500 nm).
Nanomaterials-derived products are being actively pursued for use in a wide range of applications, including electrochemical energy storage and generation, chemical sensors, optoelectronics, semiconductors, wear and scratch resistant coatings, and heat transfer. The interest stems from the fact that researchers see immense potential for improving functional properties of components and devices by nanostructuring. In some cases, the use of nanoparticles as feedstock material can facilitate processing of an improved end product at a lower cost. However, while the use of nanoparticles as starting material can lead to benefits in a number of applications, researchers must tailor the structure and composition of the starting powder in order to maximize the property enhancements and performance and realize the true potential of nanomaterials.
Over the past several years, a number of techniques have been developed for the production of ceramic nanoparticles. These include: laser ablation, microwave plasma synthesis, precipitation from a solution, spray pyrolysis, plasma arc synthesis, hydrodynamic cavitation, and gas condensation using either a physical evaporative source or chemical precursors. Vapor phase processes are capable of producing well-defined spherical nanoparticles with narrow particle size distribution. Several single component oxides can be produced by an atmospheric flame process at low cost. However, it is extremely difficult to control the composition of multi-component (two or more cations in the chemical formula) and doped (one or more cations present in the lattice of the host compound) ceramic powders because of the significant variations in the vapor pressures of different constituents. On the other hand, solution-based processes can be used to exercise excellent control on the composition, but particle characteristics are not as good as those produced by any of the vapor phase processes. The synthesis method discussed in this patent application bridges the gap between liquid and vapor phase processing routes to produce nanostructured doped/multi-component ceramic powders, such as, MgAl2O4, SiO2:Eu, LiNbO3, TiO2: Er, ZnO:Al and SnO2:Sb, with well-defined particle characteristics.
Doped and multi-component oxide nanopowders are needed in a broad range of applications. For example, polycrystalline MgAl2O4 spinel is an infrared window material, because of its excellent optical properties. This material can be used to fabricate infrared windows and domes for a variety of military applications. Infrared transparent windows can also be widely used in the commercial sector, ranging from industrial optical lasers systems to barcode readers in supermarket checkout counters. Nanocrystalline MgAl2O4 powders can be sintered to form fine grained (˜1 μm) spinel, which has the potential to possess excellent mechanical properties at ambient as well as at high temperatures. Additionally, polycrystalline spinel will be much cheaper in cost compared to sapphire: manufactured using an expensive, albeit highly optimized molten ceramic process. On the other hand, sintering powders to form polycrystalline spinel in principle is an inexpensive process.
Doped metal-oxide nanoparticles (e.g., luminescent and electrically conducting materials) with controlled particle characteristics are required in several applications, including optical displays, electrochromic devices, sensors, optoelectronic devices and several lighting applications. For example, luminescent materials, such as phosphors, are compounds that are capable of emitting visible and/or ultraviolet rays upon excitation of the material by an external energy source. Phosphor powders are used in several applications, such as liquid crystal displays, cathode ray tube (CRT), plasma displays, thick film and thin film electroluminescent displays. In order to achieve high luminescent intensity and long life time that are required in several applications, phosphor powders should possess high purity, high crystallinity, narrow particle size distribution, small particle size, spherical morphology, homogenous distribution of activator ion and low porosity. Additionally, luminescent nanopowders are desired for the development of fluorescent labels. These materials offer significant advantages over organic dyes because of their longer half life, broad excitation spectrum, narrow, symmetric emission spectrum and minimal photo bleaching.